Census 2000 - Block Part Flag Description

Block relationship files contain a part flag field associated with some 1990 and 2000 block numbers.
The part flag is stored in the 1990 tabulation block part flag, and the 2000 tabulation block
part flag fields of the record layouts. A value of "p" in any of these fields identifies block records that do not have a whole block to whole block relationship. The part flag indicator helps to explain
the different types of relationships that exist between the block identifiers. The Census Bureau has created
census block relationship information on the basis of one-to-one, one-to-many, many-to-one, and many-to-many block(s).

1. One-to-One Relationship

In some cases, a 1990 census block has a one-to-one relationship with a Census 2000 block.
Even though new block numbers have been assigned for Census 2000, the features used to define
Census 2000 blocks remain unchanged from 1990. This relationship is considered to be a one-to-one relationship.
For example, 1990 census block 101 (in census tract 16) has a one-to-one relationship with Census 2000 block 1000 (in census tract 16.01).

Example of a "one 1990 block-to one 2000 block" relationship:

11,001,001600,101,,11,001,001601,1000,

2. One-to-Many and Many-to-One Relationships

In a one-to-many relationship, a single 1990 census block is now represented by
more than one Census 2000 block. For example, 1990 block 102 (in census tract 16) is now
represented by Census 2000 blocks 1001 and 1002 (in census tract 16.01). The part flag
“p” indicates that only part of 1990 census block 102 is in each of the Census
2000 blocks 1001 and 1002.

Example of a "many 1990 blocks-to-one 2000 block" relationship:

3. Many-to-Many Relationship

A many-to-many relationship occurs when more than one 1990 census block is now represented by
more than one Census 2000 block. In this case, all 1990 census blocks and Census 2000 blocks in
question will have the part flag “p” associated with the block number. For example, 1990 census blocks 201,
202, and 203 (in census tract 16), are represented by Census 2000 blocks 5000, and 5001 (in census tract 16.01).